There was no immediate clarification. Hours earlier an Iranian Foreign Ministry spokeswoman had told The Associated Press the eight sailors had been released. However, she said it would be some hours before they were handed over to British authorities.
The British sailors were detained Monday after their three boats apparently strayed into Iranian waters on the Shatt al-Arab waterway that runs along the Iran-Iraq border.
Iran's Arabic-language TV channel Al-Alam broadcast an "urgent" caption on its screen at 12:40 p.m. EDT reading: "The second round of talks on the British detainees is postponed until tomorrow, Thursday" June 24, according to a translation provided by the British Broadcasting Corp.
The station had earlier reported the sailors' release could be delayed to Thursday. It said British and Iranian officials had been negotiating in the southwest Iranian town of Mahshahr near the spot the British servicemen were detained.
In London, the British Foreign Office said it had not been told officially that the release had been delayed to Thursday.
A British diplomat conceded, however, that as night had fallen in Iran, it was possible the release would not take place until Thursday.
Earlier Wednesday, the Foreign Office said three British diplomats were travelling from Tehran to Abadan, a port city 30 miles east of the Iraqi city of Basra, to receive the six Royal Marines and two sailors.
It's believed the men were held in Khuzestan, an extremely-hot desert-like province near the Iraqi border, Tehran reporter Ramita Narvai told CBS Radio News.
"We have got a team of three from our British embassy down there and that will be the conduit," the Foreign Office spokesman said, speaking on customary condition of anonymity.
The men were detained in the Shatt al-Arab waterway, which runs along the Iran-Iraq border as they were delivering a patrol boat for the new Iraqi river patrol service. The waterway is known in Iran as the Arvand River.
A top military official said the sailors were being released because their intrusion into Iran's waters was apparently a mistake.
The sailors were shown on Iranian television blindfolded and seated cross-legged on the ground.
"My name is Sgt. Thomas Harkins from the British Royal Marines. I do apologize for entering Iranian territorial waters," one said on Al-Alam, an Arabic-language station, reading from a prepared text.
The broadcast also showed the patrol boats and weapons it said had been confiscated from the sailors.
Iran had earlier said the men would be prosecuted.
A Foreign Ministry spokesman told AP that Iranian Foreign Minister Kamal Kharrazi played a key role in resolving the minor border incident that had threatened to turn into a major diplomatic crisis.
British Foreign Secretary Jack Straw had called Kharrazi on Tuesday to ask for the release of the sailors.
The waterway, Iraq's main link with the Persian Gulf that divides Iran and Iraq, has long been a source of tension between the neighbors. The 1980-88 Iran-Iraq war broke out after Saddam Hussein claimed the entire waterway.
Iran said the British vessels were about a half-mile inside Iranian territorial waters.
The BBC reported the servicemen were thought to come from two Scotland-based units - Arbroath-based 45 Commando and the Fleet Standby Rifle Troop from Faslane on the Clyde - and from the 539 Assault Squadron in Plymouth, south-west England.
British-Iranian relations have run hot and cold for years. The detentions follow a fresh strain after London helped draft a resolution International Atomic Energy Agency's board of governors.for past nuclear cover-ups at last week's meeting of the
Iran says its program is aimed only at producing energy, while the United States accuses Tehran of trying to develop nuclear weapons. Iran accused Britain, which it had seen as a partner in the investigation into its nuclear activities, of caving in to U.S. pressure.
Iranians repeatedly demonstrated in front of the British Embassy in Tehran last month, throwing stones at the building to protest the U.S.-led occupation of Iraq. Britain is America's main coalition partner in Iraq.
Protesters also condemned war damage to Shiite holy shrines in Iraq, demanded the expulsion of the British ambassador to Tehran and called for the embassy to be closed.
British-Iranian ties also were strained in 1989 when the founder of the Islamic revolution, Ayatollah Ruhollah Khomeini, issued a fatwa, or religious edict, against British author Salman Rushdie.
In 1998, the Iranian government declared it would not support the fatwa and the two countries exchanged ambassadors in 1999.
In 2002, Iran rejected a British candidate for ambassador, claiming he was a Jewish spy. A year later, shots were fired at the British Embassy in Tehran, after Britain briefly held an Iranian diplomat accused of helping to mastermind the car bombing of a Jewish center in Argentina.
Iran has expressed pleasure over the toppling of Saddam, but has strongly opposed deployment of U.S.-led coalition forces on its borders.